Trump feels insulted being called 'old' by Kim Jong Un

Trump's tweet was part of a series of tweets that included China's plan of "upping the sanctions" against North Korea and how Chinese President Xi Jinping wants to "denuclearize" the country.

"Reckless remarks by an old lunatic like Trump will never scare us or stop our advance".

"Do not underestimate us", Trump said Tuesday in a speech delivered to South Korea's National Assembly.

Speaking later in Vietnam's capital, Hanoi, Trump said "it would be very, very nice" if he and Kim became friends.

In his tour of Asia, Trump has warned North Korea not to stretch US patience, but also suggested the possibility of a diplomatic solution to the crisis.

Responding to the latest statement, Trump posted a tweet dripping with sarcasm: "Why would Kim Jong-un insult me by calling me 'old, ' when I would NEVER call him 'short and fat?' Oh well, I try so hard to be his friend - and maybe someday that will happen!"

Shortly after that speech, North Korean officials told CNN, "We don't care about what that mad dog may utter", referring to Trump.

Trump has traded insults and threats with Kim in the past amid escalating tension over Pyongyang's nuclear and missile programs as North Korea races toward its goal of developing a nuclear-tipped missile capable of reaching the United States -something Trump has vowed to prevent.

On Aug. 8, Trump threatened the regime with "fire and fury like the world has never seen", leading Kim to say he would consider sending missiles into the waters off the coast of Guam in "mid-August".

He said it would be a "good thing" for North Korea and the world if he and Kim could become friends, saying it "might be a odd thing to happen but it's certainly a possibility".

The US think-tank said: "Although Pyongyang is outspent by its neighbours in dollar-to-dollar comparisons and defence experts say it operates with raging equipment and technology, the regime's forward-deployed military position and missiles aimed at Seoul ensure that Pyongyang's conventional capabilities remain a constant threat to its southern neighbour".

The Trump administration has said all military options remain on the table when dealing with the North Korean threat, but top USA officials have consistently emphasized the U.S.is pursuing a diplomatically led effort, including additional economic pressure.